(MCT) — CHICAGO — The U.S. Justice Department is investigating the wrongful convictions of four men who were teenagers when they were convicted of the 1994 rape and murder of a woman based largely on confessions later proven to be false, the Cook County state’s attorney’s office said.

The civil rights investigation has been going on for some time, but it is not clear if it is related to a Justice Department investigation involving Chicago police detectives who obtained confessions that have turned out to be false — often after being undermined by DNA evidence.

Why the Justice Department would focus on the 1994 among the many false-confession cases in Cook and surrounding counties is also unclear.

The case turns on the rape and murder of Nina Glover, 30, who was found strangled in a trash bin in Chicago’s Englewood neighborhood. The four teenagers — Terrill Swift, Harold Richardson, Michael Saunders and Vincent Thames — were charged after Chicago police obtained confessions.

After serving 15 years in prison, Swift was released and sought DNA testing to prove his innocence and identify the murderer. That testing linked semen found at the crime scene to convicted murderer Johnny Douglas, who was killed in 2008.

Prosecutors opposed exonerating the four, arguing that Glover’s history of trading sex for drugs made it possible that she had consensual sex with Douglas. Chief Criminal Court Judge Paul Biebel, however, threw out the convictions last year, and prosecutors decided not to retry the cases against the men.

Last month, the four filed separate lawsuits in federal court alleging that police and prosecutors essentially framed them for Glover’s murder. The defendants include James Cassidy and Kenneth Boudreau, detectives who have been linked to a number of cases involving false confessions. Cassidy and Boudreau could not be reached for comment.

The Justice Department did not respond to a request for comment.

Joshua Tepfer, the lawyer who helped Swift obtain testing and prove his innocence, welcomed the news of the federal investigation.

“Whenever there’s a wrongful conviction, especially with a false confession ... it’s essential that we examine what went wrong,” said Tepfer, an attorney at the Center on Wrongful Convictions at Northwestern University’s law school. “Terrill Swift was the victim of a tragic injustice.”